Huh? I just tried tagging a message, which opens a popup for Telegram Premium. Also web search brings up "Tags are already available to all Telegram Premium users." from Telegram website - it's an old post, but I don't see anything anywhere that says otherwise. Or do you mean #hashtags?

They're (OP) almost definitely referring to their own service which has tagging built in for free.

oh, you were talking about Telegram. I misunderstood it. My bad.